1. Field of the Invention
The present invention relates to an image reading apparatus and, more particularly, to an image reading apparatus for continuously carrying sheet-like originals, and for reading one or both faces of the carried original images using image sensors arranged along a carrying path.
2. Related Background Art
In recent years, various image data file systems have been proposed. In an image data file system of this type, image data is stored in a file medium such as an optical disk or an optomagnetical disk, the stored image data is retrieved and read out as needed, and the readout image data is reproduced, i.e., printed or displayed.
In order to deal with a dual-face original, the file system comprises an original carrying/reading mechanism. In this mechanism, a single original is carried twice, so that its front face is read first, the original is then reversed, and thereafter, its back face is read. Alternatively, the mechanism is provided with a carrying path having a length twice or more the length of an original to be read, so that the front face of an original is read in the first half of the carrying path, and the back face of the original is then read in the second half of the carrying path.
In the above-mentioned arrangement, images on both the faces can be read. However, in the former twice-carrying type mechanism, in order to read a dual-face original, the original must be manually inserted twice, or a mechanism for automatically inserting the original in a reading unit arranged along the carrying path twice must be arranged. In either case, the sheet insertion operation requires a time twice or more that of a conventional sheet insertion operation. When the mechanism for automatically inserting an original twice is arranged, the arrangement of the original carrying path is complicated, and this leads to not only an increase in manufacturing cost of the system but also an increase in frequency of original jamming.
On the other hand, since the latter single-carrying type mechanism requires the carrying path having a length twice or more that of a conventional mechanism, the sheet insertion operation requires a time twice or more that of a conventional sheet insertion operation, and the size of the system itself undesirably becomes bulky.
Thus, an image reading apparatus, in which two image sensors (solid state image pickup elements such as CCD (charge-coupled device) line sensors) are arranged above and below a carrying path for carrying a sheet-like original as means for easily inputting original data on a dual-face original at high speed, and images on both the front and back faces of the dual-face original are continuously read within one scan line at the same time to perform the subsequent image processing, has been put into practical applications.
However, the above-mentioned image reading apparatus reads two faces of an original which has effective image data on only one face, and image data on an unnecessary face is stored in a file medium such as an optical disk or an optomagnetical disk, thus considerably impairing storage efficiency of a file device.